JPS6334896A - Discharge lamp lighter - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a discharge lamp lighting device for lighting a high-pressure discharge lamp using a chopper method.

(Background Art) Conventionally, there is a discharge lamp lighting device that lights a high-pressure discharge lamp 3 using a chopper as shown in FIG. Power terminal 1, 2
A DC power supply with the polarity shown is connected between them. This DC power supply includes a switching element Q1 consisting of a transistor, an inductance element R, and a current detection resistor R.
A high pressure discharge lamp 3 is connected via s. A high frequency bypass capacitor CI is connected in parallel to the series circuit of the high pressure discharge lamp 3 and the current detection resistor R8. Also,
A flywheel diode D is connected in parallel to the series circuit of the inductance element L1 and the capacitor C5, forming a step-down chopper circuit. The switching element Q is driven by a base drive circuit 4. An on/off control signal created by the control section 11 is input to the base drive circuit 4 .

The control unit 11 controls the lamp current IN' flowing through the high pressure discharge lamp 3.
a is detected by the voltage VR5 across the resistor Rs, and depending on the magnitude of the detected lamp current 11a, the switching element Q1
The on-time To is controlled, and a substantially constant current is caused to flow through the high-pressure discharge lamp 3. In the control section 11, the differential amplifier reference voltage VR□ and the detection voltage VR5 are compared and amplified. The output of the differential amplifier 9 is input to the comparator 7 and compared with the output of the reference waveform oscillator 10. The reference waveform oscillator 10 outputs a triangular reference waveform with a frequency determined by the time constant of the resistor R5 and the capacitor C2. The comparator 8 compares the reference voltage obtained by dividing the reference voltage vFlQF with the resistors R2 and R1 with the output of the reference waveform oscillator 10, and limits the maximum on-time of the switching element Q. In this conventional example,
The maximum value of the on-time TON is 50% on-duty. Here, the on-duty D is (T ON/
T ) x 100, where T is the reference waveform oscillator 1
It is the reciprocal of the oscillation frequency of 0. The outputs of the comparators 7 and 8 are used as trigger inputs of the flip-flop circuit 5 via the OR gate 6. Base drive circuit 4 drives switching element Q1 by the output of flip-flop circuit 5. When the high pressure discharge lamp 3 is lit by such a discharge lamp lighting device, the following pressure is generated.

When the high-pressure discharge lamp 3 is used for a long time, the electrodes are worn out, the arc tube becomes black, and the coldest point temperature rises, causing the lamp voltage V1a to rise. When the lamp voltage Vim increases, in the above operation, the switching element Q is controlled to keep the lamp current Ila constant, so the lamp power Wl'a increases by the amount that the lamp voltage Vln increases. As the lamp power WVa increases, stress on the arc tube increases, which may lead to damage in the worst case. If the lamp is lit at a commercial frequency, it will go out due to the restriking voltage, but with the chopper lighting method shown in Figure 7, it is difficult for this to go out, so the lamp voltage
Even if 1a becomes extremely high, the lighting condition is maintained, and damage to the arc tube itself due to stress becomes a problem.

Conventionally, as a countermeasure against this problem, a maximum value of the ON time of the switching element Q1 is set by the comparator 8 of the circuit shown in FIG. 7, and constant current control is not possible beyond that value. This control characteristic is shown in Fig. 8. In Fig. 8, the horizontal axis shows the on-duty D, and the vertical axis shows the lamp voltage V.
I'm taking la. ■3 is the rated lamp voltage of high pressure discharge lamp 3, V62 indicates the voltage at no load, Vlm is 1
．． 3 At around V3, on-duty D becomes 50%,
Even if the lamp voltage Vla becomes higher than that, the on-duty D is maintained at 50% and is prevented from becoming larger than 50%. This method can suppress the increase in lamp power, but since it continues to be lit even at the end of its life, the stress on the arc tube is reduced, but if this condition continues for a long time, the arc tube will There is still a risk of damage.

Also, when the lamp voltage ■la reaches 1.3V, the eighth
As shown by the broken line in the figure, immediately reduce the on-duty D to 0%.
It is also possible to forcibly turn off the high-pressure discharge lamp 3 by turning the high-pressure discharge lamp 3 off, but with this method, when the lamp voltage V1m temporarily increases, a malfunction that turns off the lamp is likely to occur even when the lamp is normal. For this reason, there is a problem in that there is no freedom in circuit design and the precision of the parts must be increased.

(Object of the invention) The present invention has been made in view of the above points, and
The object thereof is to provide a discharge lamp lighting device that can prevent damage to the arc tube by suppressing overload caused by an increase in lamp voltage of a high-pressure discharge lamp.

(Disclosure of the Invention) As shown in FIGS. 1 to 6, the discharge lamp lighting device according to the present invention includes a high-pressure discharge lamp 3 whose impedance increases with time and a high-pressure discharge lamp 3 that The switching element Q1 that cuts off the supplied current and the detected amount (VH9) of the lamp current lff1a flowing through the high pressure discharge lamp 3
), the discharge lamp lighting device comprises a controller 11 that controls a switching element Q so that the power supplied to the high-pressure discharge lamp 3 is stabilized according to A high first voltage value (e.g. 1
．． 3VZ) or more, the on-duty D is fixed at the maximum on-duty Dmax (for example, 50%), and when the lamp voltage Vla becomes more than a second voltage value that is higher than the first voltage value (t, 3v*), the on-duty D is fixed. A protection circuit 13 is provided to lower the voltage.

FIG. 1 shows an example of the relationship between on-duty D and lamp voltage VZa in the present invention.

In FIG. 1, the operating point a is the lamp voltage Vl! This is the point in time when a increases and the on-duty D reaches the maximum on-duty Dmax. From operating point a to operating point )), lamp voltage V1a is maintained at maximum on-duty D wax.
This is a period in which the temperature rises and the ramp T and flow INa fall. At the time of operating point C, it is determined that the life of the lamp has expired, and the lamp shifts to operating point C, and the on-duty is set to 0%.

FIG. 2 shows another example of the relationship between the on-duty D and the lamp voltage Vl'a in the present invention. The difference from Fig. 1 is that at operating point C, the on-duty is several % to 2
The advantage is that even if the lamp goes out in this state and becomes unused, the switching element Q1 is still operating, so when a new lamp is installed, it can be turned on immediately. be.

In this way, the present invention sets the maximum on-duty 4p+na×, and increases the lamp voltage ■la to increase the on-duty D.
Even if the on-duty D reaches the maximum on-duty D max, the maximum on-duty D max is maintained for a certain increase in the lamp voltage V1a, and after the lamp current has decreased to a certain extent during this period, the on-duty D is set to 0% and the light is turned off. or on-duty D of several to 20%.
This is characterized by reducing the lamp power to a level that does not cause damage to the arc tube.

Hereinafter, specific examples of the present invention will be described.

Figure 3 shows an embodiment of the present invention. The circuit of this embodiment operates according to the graph in FIG.

The circuit of this embodiment has a protection circuit 13 in addition to the conventional circuit shown in FIG.
is added. The detection voltage VftS from the resistor Rs is input to the comparator 12 in the protection circuit 13, and is proportional to the reference voltage "RE!F2".Vps
< V REF2, the output of the comparator 12 becomes "Hi B b" level, and the output of the
The base potential of , increases, and transistor Q turns on. When transistor Q is turned on, the anode potential of diode D is lowered, so transistor Q2 is turned off. When transistor Q is off, resistor R
Since the anode potential of the diode D2 is increased by the power supply voltage VcC via the transistor Q4, the transistor Q2 is turned on. Transistor Q2 is connected in series with resistor R1 in a voltage divider circuit consisting of resistor R2 and resistor R, and when transistor Q2 is on, voltage VRIEF is divided by resistors R2 and R-, and the seventh The operation is the same as that of the conventional example shown in the figure, but when the transistor Q2 is turned off, the voltage ■RεF is input as is to the comparator 8 without being divided by the resistors R2 and R3.
The output of is always at the °''■ - gh'' level, and the on-duty of the switching element Q1 is 0%.

Hereinafter, the operation of the circuit shown in FIG. 3 will be explained by dividing it into operating points a, b, and c in the graph of FIG. 1.

(i) Period up to operating point a In normal operating conditions, operating point a in FIG. 1 is not reached. At this time, since the lamp current Ila is flowing sufficiently, V R9> V R1::F2
Therefore, the output of the comparator 12 is at "Low" level. Therefore, when transistor Q is off and transistor Q2 is on, the same control characteristics as the conventional control characteristics shown in FIG. 8 can be obtained.

i) Period from operating point a to operating point During this period,
Then, the lamp voltage Vea increases and the lamp 7M, current 1
1& goes down, and the output of the differential amplifier 9 goes down. Therefore, the on-duty D of the switching element Q1 is determined only by the output of the comparator 8, and the on-duty D is fixed at the maximum on-duty DIIax.

The operation at this time is shown by the solid line in FIG. In FIG. 4, (A> indicates the oscillation output waveform of the reference waveform oscillator 10, which is a sawtooth triangular wave. This waveform (A>
is compared with a voltage (B) obtained by dividing voltage VREF by resistor R2 and resistor R2 by comparator 8. The timing at which the switching element Q1 turns on is shown in Fig. 4 (
As shown in b), this is only during the period when the reference waveform (A) is higher than the voltage (B). On duty D at this time
is set to 50%.

(iii) At the time of transition from operating point S to operating point C, lamp voltage VIa further increases, and when lamp voltage ■ea approaches operating point C, lamp current Ila further decreases, and the output of comparator 12 becomes "High". Transistor Q is turned on by reaching the level
2 is off. As a result, the on-duty D moves from operating point A to operating point C in FIG.

The operation at this time is shown by broken lines in (a) and (b) in FIG. By turning off the transistor Q2, the input of the comparator 8 substantially has a voltage VR1! F is applied as it is to the level (Bo), and since this value is set higher than the peak value of the sawtooth reference waveform (A), the switching element Q remains off.

By the above-described operation, in this embodiment, the lamp voltage Vl
When a increases and becomes, for example, 1°3 times the lamp voltage 1a, the on-duty is prevented from becoming greater than 50% and the on-duty is switched from constant current control to constant on-duty control, and the lamp voltage Vt' a
When the lamp current (1a) increases, the lamp current (1a) decreases, and when it falls below a predetermined value, the operation of the switching element Q is stopped and the high-pressure discharge lamp 3 is forcibly turned off.

K1 Takumi 1 Figure 5 shows another embodiment of the present invention. The circuit of this embodiment operates according to the graph in FIG.
This is the magnitude of on-duty D when transitioning to . That is, in this embodiment, at the operating point C, the
The on-duty is set to about %. In this way, since the switching element Q is in operation even when there is no load, there is an advantage that the lamp can be turned on immediately after replacing it.

In the embodiment circuit shown in FIG. 5, the main circuit is the same as the conventional circuit in section 7. 1gIm section 11 includes a protection circuit 13.
is added. The voltage VR6 of the current detection resistor R9 is a differential tt! formed by an operational amplifier to which resistors RIG and R11 are added. ! It is amplified by the amplifier 9, and the output power is 31 degrees! In fF, the on-duty is controlled by the comparator 7. During the period when the lamp current 11a is sufficiently flowing, the voltage VR5 is large and the output of the differential amplifier 9 is high, so that the capacitor C is charged via the diode D1 and the resistor RIl. This full S! A base current is supplied to the transistor Q through the resistor R3 by the voltage, and the transistor Q is turned on. In this state, both ends of resistor R7 are short-circuited, so
The same operation as the conventional example can be obtained. In addition, the lamp current 11a
When the voltage VR5 decreases, the output of the differential amplifier 9 decreases, so the charging voltage of the capacitor C1 decreases, and the base current is no longer supplied to the transistor Q4, turning off the transistor Q4. In this state, the resistor R2 is connected in series with the voltage dividing resistor R6.

The reference voltage input to comparator 8 becomes higher.

The operation of the circuit shown in FIG. 5 will be explained below by dividing it into operating points a, b, c, and d in the graph shown in FIG.

(i)! Period up to pH operating point a Under normal operating conditions, the operating point a in FIG.
The duty is controlled by the output of the transistor Q4, and while the capacitor C1 is charged by the diode D and the resistor R8 by this output, the transistor Q4 is kept in the on state, and the resistor R
1 is short-circuited by a transistor Q. Therefore, during this period, the same control characteristics as those of the conventional example shown in FIG. 8 can be obtained.

(ii) Period from operating point a to operating point JtII
During this period, the lamp voltage ■ia increases, the lamp current Ila decreases, and the output of the differential amplifier 2S9 decreases, but the transistor Q still maintains the on state. As the output of the differential amplifier 9 decreases, the on-duty is determined by the output of the comparator 8 instead of the comparator 7, and the on-duty D is determined by the maximum on-duty Dm.
ax (for example, 50%). The operation at this time is
It becomes as shown by the solid line in FIG. The level (B) of the reference voltage input to the comparator 8 is the transistor Q.

is on, so VR Kano
).

(iii) When transitioning from operating point S to operating point C, lamp voltage Vffia further increases, and lamp voltage ■I! When a approaches the operating point, the lamp current D1II further decreases, so the output of the differential amplifier 9 further decreases, transistor Q no longer remains on, and transistor Q4 turns off at the operating point. . At this time, level (B)
Since the resistor R7 is connected in series with the resistor R3, the level (B') shown by the broken line in FIG. 6 = VRcr×
(R3+R?)/(R20Rx+R?),
The on time of the switching element Q is very short.

(iV) When transitioning from operating point C to operating point dl\ Even if the lamp goes out at operating point C, transistor Q is off and maintains the level (B"), so it becomes operating point d in Figure 2, and the new When the lamp is installed, it starts and goes into normal operation.In this embodiment, the output of the differential amplifier 9 that controls the on-duty is also used as the control signal for the transistor Q4, so the A circuit element corresponding to the comparator 12 in the circuit is not required.

In the above embodiment, the frequency (1,/T'') is constant and the on-duty D is controlled by changing the on-time ToN, but a method of changing the off-time TOFF may also be used. In addition, although each of the above embodiments describes a DC chopper lighting method, if the lighting method detects the current and controls the switching element, thereby increasing the lamp voltage and causing an overload, The effects of the present invention can be sufficiently obtained, and it can be applied to, for example, a system in which a full bridge inverter operating at a low frequency is added to a step-down chopper to supply power to a lamp.

<Effects of the Invention> As described above, in the present invention, in a device for lighting a high-pressure discharge lamp whose impedance increases over time by a switching element controlled according to the detected amount of lamp current, the lamp voltage is When the lamp voltage exceeds a first voltage value that is higher than the rated lamp voltage, the on-duty of the switching element is fixed to the maximum on-duty, and when the lamp voltage reaches a second voltage value that is higher than the first voltage value, the on-duty of the switching element is fixed. Since it is equipped with a protection circuit that lowers the on-duty, by providing some play between when the on-duty reaches the maximum and when the on-duty is reduced, a normal high-pressure discharge lamp can be judged to be abnormal and turned off. This has the advantage that overload damage to the high pressure discharge lamp can be reliably prevented without causing any malfunction. In addition, in the play motion area,
Since the on-duty is constant, the lamp current decreases as the lamp voltage increases. Therefore, it is possible to provide a leeway in the design for the point in time when the protection circuit is activated, increasing flexibility in the design and There is an advantage that the first and second voltage values may also be set relatively roughly.

Furthermore, as stated in the explanation of the control characteristics in Fig. 2,
Do not immediately set the duty at no load to 0%, but set it to 26 to 2.
Setting it to a low level of about 0% has the advantage of being able to turn on the lamp immediately when replacing it, and also shortens the period during which the switching element is turned on when the lamp is in a negative light state, reducing the switching element's time. This has the advantage of requiring less drive current.

[Brief explanation of drawings]

FIG. 1 is a diagram showing control characteristics in a discharge lamp lighting device according to one embodiment of the present invention, FIG. 2 is a diagram showing control characteristics in a discharge lamp lighting device according to another embodiment of the present invention, and FIG. 1 is a circuit diagram showing a specific circuit of the embodiment shown in FIG. 1, FIG. 4 is an explanatory diagram of the same operation, FIG. 5 is a circuit diagram showing a specific circuit of the embodiment shown in FIG. FIG. 7 is a circuit diagram of a conventional example, and FIG. 8 is an explanatory diagram of the same operation. 3 is a high pressure discharge lamp, 11 is a control unit, 13 is a protection circuit, Ql
is a switching element.

Claims (1)

[Claims] (1) A high-pressure discharge lamp whose impedance increases over time, a switching element that cuts off the current supplied from the power supply to the high-pressure discharge lamp, and a switching element that changes the impedance to the high-pressure discharge lamp according to the detected amount of lamp current flowing through the high-pressure discharge lamp. In a discharge lamp lighting device comprising a control section that controls a switching element so that the supplied power is stabilized, when the lamp voltage exceeds a first voltage value higher than the rated lamp voltage, the on-duty of the switching element is reduced. A discharge lamp lighting device comprising: a protection circuit that fixes the on-duty of the switching element to a maximum on-duty and lowers the on-duty of the switching element when the lamp voltage exceeds a second voltage value higher than the first voltage value.